Marine engines used to power watercraft can be generally classified as either being an inboard, outboard, or stern drive. An inboard engine is located inside of the watercraft and poses certain design challenges. For example, an inboard engine is generally confined to a small space in which air flow is limited. Limitations of air flow around the engine require a sufficient cooling arrangement be in place in order to handle heat generated during use. Further, as the engine is operated in a marine environment precautions must be taken in order to prevent water from finding its way inside of and consequently damaging the engine.
One type of inboard marine engine employed on watercraft is a twin head engine. This type of engine features cylinders that are located on opposite sides of the engine that generate exhaust gases upon firing. Manifolds are commonly employed in order to channel the exhaust gases into a single stream on one side of the engine and into a single stream on the opposite side of the engine. The two exhaust gas streams may then be routed to a discharge point from which the exhaust gases can exit the watercraft. Alternative arrangements are known in which the two separate exhaust gas streams are combined into one stream and subsequently routed to a discharge point. The two manifolds are designed in order to inhibit the movement of water through the manifolds and into the inboard engine.
The gas streams can be transferred from the manifolds in jacketed conduits. A cooling fluid, such as water or antifreeze, is transferred through the jacketed conduits and kept separate from the gas streams in order to draw heat from the gas streams and cool the exhaust system. The cooling fluid is inserted into the conduits proximate to the manifolds and flows in the same direction through the conduits as does the exhaust gases. It may be the case that cooling fluid is not present at certain locations of the conduits. For example, the top of the conduits may not have cooling fluid present due to the fact that the cooling fluid is drawn by gravity down to the bottom of the conduits as the cooling fluid flows therethrough. Further, the orientation of the conduits themselves may be provided so that certain portions are void of cooling fluid. The absence of cooling fluid at certain locations leads to the formation of hot spots on the conduits at these locations. Hot spots may result in the burning of individuals should they come into contact therewith. Further, hot spots may cause a fire aboard the watercraft, and hot spots could lead to a weakening of components of the exhaust system which may cause it to fail. As such, there remains room for variation and improvement within the art.